When the PN junction plus reverse voltage, that is, the positive pole of the power supply connected to the N area, the negative then P area. The direction of the applied electric field is the same as the direction of the electric field in the PN junction, and the PN junction is in the reverse bias. Under the action of the reverse voltage, the holes in the P region and the electrons in the N region will further leave the PN junction, so that the thickness of the depletion region is widened and the internal electric field of the PN junction is strengthened.
This result, on the one hand, makes it difficult for the majority of the carriers in the P and N regions to cross the barrier, and the diffusion current approaches zero. On the other hand, due to the enhancement of the internal electric field, the minority carriers in the N region and the P region are more likely to generate drift motion. In this way, the current flowing through the PN junction is determined by the dominant drift current. The drift current is shown on the external circuit with a reverse current IR flowing into the N region.
Since the minority carriers are generated by the intrinsic excitation, the concentration is very small, so IR is very weak, usually the order of microanian. When the tube is made, the IR value is determined by the temperature, almost independent of the applied voltage. IR is affected by temperature, in some practical applications, must also be considered. PN junction in the reverse bias, IR is very small, PN junction presents a large resistance, it can be considered that it is basically non-conductive.